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Better JTextField

How can I create a JTextField that accepts only a predefined length of characters, or accepts only numbers?

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gadio

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incah

ASKER

You mean a DocumentListener. There is no TextListener for a JTextField. Anyway I did it in the following code,but it doesn't work as expected. When the first non-digit character is entered the program that uses the NumberJTextField freezes. But even if it worked I can't find of a nice way to change the content of the field (see method doWork() which removes the entire contents and inserts a new String. There I'm forced to pass null as the third parameter to insertString() because I don't know what else to pass).

import com.sun.java.swing.*;
import com.sun.java.swing.text.*;
import com.sun.java.swing.event.*;

public class NumberJTextField extends JTextField {
      public NumberJTextField() {
            super();
            this.getDocument().addDocumentListener(new MyDocumentAdapter());
      }
      public NumberJTextField(String text) {
            super(checkedString(text));
            this.getDocument().addDocumentListener(new MyDocumentAdapter());
      }
      public NumberJTextField(int columns) {
            super(columns);
            this.getDocument().addDocumentListener(new MyDocumentAdapter());
      }
      public NumberJTextField(String text,int columns) {
            super(checkedString(text),columns);
            this.getDocument().addDocumentListener(new MyDocumentAdapter());
      }
      public NumberJTextField(Document doc,String text,int columns) {
            super(doc,checkedString(text),columns);
            this.getDocument().addDocumentListener(new MyDocumentAdapter());
      }
      private static String checkedString(String text) {
            if (text==null || text.equals(""))
                  return(text);
            int len=text.length();
            StringBuffer out=new StringBuffer(len);
            char c;
            for (int i=0;i<len;i++) {
                  c=text.charAt(i);
                  if (c>='0' && c<='9')
                        out.append(c);
            }
            return(out.toString());
      }
      public void setText(String text) {
            super.setText(checkedString(text));
      }

      class MyDocumentAdapter implements DocumentListener {
            public void insertUpdate(DocumentEvent e) {
                  doWork(e);
            }
            public void removeUpdate(DocumentEvent e) {
            }
            public void changedUpdate(DocumentEvent e) {
                  doWork(e);
            }
            private void doWork(DocumentEvent e) {
                  Document doc=e.getDocument();
                  int len=doc.getLength();
                  if (len>0) {
                        try {
                              String text=doc.getText(0,len),
out=checkedString(text);
                              if (!text.equals(out)) {
                                    doc.remove(0,len);
                                    doc.insertString(0,out,null);
                              }
                        } catch(BadLocationException ble) {
                        }

                  }
            }
      }

}